Materials, Their Taxonomy and Natural History 69 



First larval stage: Head, pronotum, and legs dark brown, or rarely black; 

 body pale lavender or yellowish, spiracula spots alone present, small. Length 

 at end of stage, 2.5 to 3.5 mm. 



Second larval stage: Exactly like first. Length at end of stage, 3 to 4.5 mm. 



Third larval stage (plate 7, fig. 7) : Strongly resemble small larvae of L. 

 texana, color variable, pale dilute lavender to pale bluish-yellow ; pronotum and 

 head often broAvn or yellow-brown; legs variable, brown to black. Length at 

 end of stage, 5 to 8.5 mm. Length of larval life, 10 to 18 days; average about 

 14 days. 



Pupa: Pupates in g-round from 0.5 to 2 inches below the surface. Pupa 

 yello w- white ; pupation lasts 6 to 12 days ; average 8 days. 



Length of ontogeny: 25 to 40 days; average about 30 days. 



Geographical Distribution : Limited to desert areas of Arizona and Sonora. 

 Recorded from Hermosville, Guaymas, and Nogales, State of Sonora, Mexico; 

 Benson, Tucson, and Maricopa, Arizona. 



Habitat, ecology, life-history : Apparently there is but one generation per 

 year of this form. This has been our experience at Tucson and in cultures. 

 Hibernates as an imago. 



Source of material: Bottoms of Santa Cruz River in moist midsummer at 

 foot of Tumamoc Hill, Tucson, Arizona. 



EVOLUTION AND PHYLOGENY OF THE LINEATA GROUP. 



The present conditions in any group or organisms in nature afford little basis 

 for creating schemes of descent, and where fossil evidence is lacking the usual 

 substitute of ontogenetic stages, similarities, distribution phenomena, and the 

 like usually result in expressing the bias of the student rather than relation- 

 ships. To many this procedure is proper and correct, and many believe it is 

 still able to give accurate pictures of descent. When applied to large groups 

 and longer trends of evolutionary development this may in a very crude manner 

 be partly true, but for minor groups and for the building of schemes of relation- 

 ships within genera the method can hardly be considered as safe. Former 

 methods and consideration in phylogeny were based upon the unproven assump- 

 tion that descent had always been by dichotomy, either by slow divergent 

 variations and extermination of intermediates or by a saltation, both a dichot- 

 omy of existing materials, and so grew up the familiar tree-like schemes of 

 descent, but to what extent these represent the truth no one at present can 

 honestly decide. 



The accumulated experience of the neo-Mendelian investigations shows be- 

 yond doubt that attributes and qualities can be and are shifted about, replaced, 

 and recombined, giving quite different expressions to the new combinations. 

 As a result nothing new appears; only an organic metathesis occurs, which, 

 nevertheless, produces distinct, divergent, individual entities. To what extent 

 are the grouped lines of descent which we call species the product on a larger 

 scale of metathesis in nature ? Who can answer ? The Linngean view that cross- 

 ing is indicative of and synonymous with degeneration in standard and stamina 

 in the species is hardly tenable at this time, and in the attempt to arrive at some 

 comprehension of the probable past history one can not forget the part that 

 crossing may have played in conjunction with other processes in the formation 

 of the evolved group. 



